Describe the major pollutants of water.

Introduction: Water Pollution is the physical, chemical, or biological alteration in water quality that renders it harmful for human consumption and aquatic life. Water pollutants originate from point sources (factories, municipal drains) and non-point sources (agricultural runoff).

1. Classification and Description of Major Water Pollutants:

• 1. Biological & Pathogenic Agents:
  • Coliform bacteria (Escherichia coli), viruses, protozoa, and parasitic worms entering water from untreated domestic sewage and animal waste, causing cholera, typhoid, and hepatitis.
• 2. Oxygen-Demanding Organic Wastes:
  • Organic sewage, distillery effluents, and food-processing wastes. Their decomposition by aerobic bacteria drastically depletes Dissolved Oxygen (DO $<4 ext{ mg/L}$ raises Biological Oxygen Demand - BOD), suffocating aquatic fish life.
• 3. Toxic Heavy Metals & Chemical Compounds:
  • Arsenic: Causes skin lesions and Blackfoot disease.
  • Lead ($Pb$): From battery/paint effluents causing severe neurological damage.
  • Mercury ($Hg$): Triggers deadly Minamata Disease through bioaccumulation.
  • Cadmium ($Cd$): Causes painful bone disease Itai-Itai.
  • Fluoride: Causes dental and skeletal fluorosis.
• 4. Agro-Chemical Nutrients (Eutrophication):
  • Excessive synthetic nitrates and phosphates from agricultural fertilizers causing massive Algal Blooms (Eutrophication), choking aquatic ecosystems.
• 5. Thermal and Radioactive Pollutants:
  • Discharge of superheated cooling water from thermal/nuclear power plants reducing dissolved oxygen; radioactive mining waste ($Uranium, Radium$).

Conclusion: Strict enforcement of the Water (Prevention and Control of Pollution) Act, 1974 and universal installation of Effluent Treatment Plants (ETPs/STPs) are vital to preserve water quality.